Air Cooling Unit For Data Centers

ABSTRACT

An air handling unit utilizing a humidifier in conjunction with a heat exchanger to provide a means for free cooling recirculating return air with evaporatively cooled outside air. A first air stream comprising outside air can be circulated through the evaporative humidifier and a first portion of the energy recovery heat exchanger, while a second air stream comprising recirculated inside air can be circulated through a second portion of the heat exchanger. The outside air will be humidified as it circulates through the humidifier, thereby cooling the outside air to its adiabatic saturation temperature. The heat exchanger will cool the recirculating inside air with the evaporatively cooled outside air.

I. CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application Ser. No. 61/491,057 filed May 27, 2012.

II. BACK GROUND

Data centers—facilities that primarily contain electronic equipment used for data processing, data storage, and communications networking—have become common and essential to the functioning of nearly every sector of the economy to aid business processes, information management, and communications functions. Increasing demand for computer resources has led to significant growth in the number of data center servers, along with a considerable increase in the energy used by these servers and the cooling infrastructure that supports them. The cooling infrastructure for data centers is estimated to account for 50 percent of the total energy consumption of data centers. See U.S. EPA Report to Congress on Server and Data Center Energy Efficiency, Public Law 109-431 (August 2007).

The continuous operation of the electronic equipment generates a significant amount of heat. The role of data center air-conditioning systems is to remove this heat from the data center to keep the components of the electronic equipment within the manufacturers' specified temperature and humidity ranges. Cooling in data centers is often provided by computer room air conditioning units, where the entire air handling unit is situated on the data center floor. The air handling unit contains fans, filters, and cooling coils and is responsible for conditioning and distributing air throughout the data center. In most cases, air enters the top of the air conditioning unit and is conditioned as air passes across coils containing chilled water pumped from a chiller located outside of the data center room. The conditioned air is then supplied to the electronic equipment (primarily servers), typically through a raised floor area. Fans within the servers pull the conditioned air through the servers. The warmed air then stratifies toward the ceiling and eventually makes its way back to the air conditioning unit intake. Most air circulation in data centers is internal to the data center zone. To maintain a controlled environment, the majority of data centers are designed so that only a small amount of outside air enters.

Due the increased energy and capital costs associated with the expanded use of computer resources, there has been mounting interest in opportunities for energy efficiency in the information technology (IT) industry. Air-side economizers are increasingly being considered as a viable option for lowering the energy usage of a data center's cooling infrastructure. An air-side economizer is a type of air handling unit which takes advantage of cold outside temperatures to provide “free cooling” cycles that reduce or eliminate the need for the mechanical air cooling (i.e., cooling via compressors, chillers, cooling media pumps, etc.) employed by traditional data center air-conditioning systems.

Given that a data center must run continuously for a total of 8,760 hours per year, significant energy savings can be achieved with a typical air-side economizer when the outside air conditions fall within the allowable ranges. However, the operating hours of an air-side economizer are dependent on the outside air conditions—namely, the air temperature and air humidity. An air-side economizer can provide free cooling any time the outside temperature is below the required supply temperature and below the required supply dew point for the controlled environment. The economizer cycle can provide partial free cooling by reducing the mechanical cooling load when the outdoor temperature is higher than the required supply temperature but the outdoor air dew point is less than the dew point of the return air. In the context of data centers, the American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) has provided the following recommended and allowable temperature and humidity ranges for data centers:

Recommended Allowable Temperature 18-27° C. (64.5-80.6° F.) 15-32° C. (59-90° F.) Humidity 5.5-15° C. Dew Point 20%-80% Relative (41.9-59° F.) Humidity

See “Thermal Guidelines for Data Processing Environments”, ASHRAE Technical Committee 9.9 (2004).

Air-side economizers typically are integrated with a mechanical cooling system in order to assure the environmental integrity of the controlled environment regardless of the outside air conditions. A typical air-side economizer unit is shown in FIG. 1. The flow of air within the ducts of the air handling unit 1 is controlled by dampers 10, 11, and 12. Cooling coils 15 can be positioned within the air handling unit 1 to provide mechanical cooling when needed. An automated control system allows the economizer to operate in various modes depending on the outside air conditions, thereby optimizing the free cooling potential of the air handling unit while preserving the controlled environment. For instance, during cool weather, the air handling unit 1 can operate in full economization mode. In this mode, the air handling unit 1 can achieve the targeted supply air temperature without mechanical cooling by modulating the outside air damper 10 and the return air damper 11 to achieve the appropriate mix of cool outside air and warm return air. During mild weather, the air handling unit 1 operates in partial economization mode. In this mode, the outside air can provide some cooling capacity, but not enough to satisfy the entire cooling load. Thus, mechanical cooling is required to supplement the economizer cooling provided by the outside air.

Air-side economizers have proven to be an effective tool in reducing energy usage in cool climates and mild climates having low humidity. However, the efficiencies provided by current-generation air-side economizers are significantly reduced or altogether eliminated in humid climates. Humidity control is a concern for conditioned spaces, particularly in data centers containing electronic equipment. Exposing electronic equipment to overly humid outside air can cause condensation to form on the equipment, thereby negatively affecting the equipment's performance and/or causing premature equipment failure. In cool, humid climates, air-side economizer units can utilize dehumidifiers to remove moisture from the outside air before introducing the air to the conditioned space. However, dehumidifiers consume a considerable amount of energy themselves, thus diminishing the overall efficiencies achievable with the economizer unit. In warm, humid climates, dehumidification is not a viable option. The dehumidification of the outside air in the air handling unit is an adiabatic process. As latent heat is removed from the outside air, the sensible heat of the outside air will rise. Thus, the dehumidification of the warm outside air will increase the temperature of the outside air, thereby reducing or eliminating the free cooling potential of the outside air.

Accordingly, there is a need for a new air handling unit capable of efficient, economizer operation in humid climates.

III. SUMMARY

The invention disclosed herein is directed to an air handling unit which utilizes evaporatively cooled outside air as a cooling medium to cool return air recirculating in a conditioned space. Because the outside air is not introduced into the conditioned space, the air handling unit of the present invention is capable of economizer operation in conditions where the outside air humidity is above the targeted humidity level for the conditioned space.

An air handling unit having features of the present invention can comprise a humidifier positioned in a first air stream and a heat exchanger positioned partially in the first air stream and partially in a second air stream. The first air stream can be humidified as it circulates across the humidifier, thereby cooling the first air stream up to its adiabatic saturation temperature—the temperature that the air stream would achieve if it were allowed to become saturated adiabatically. The first air stream—which is now at its maximum free cooling potential—can then be circulated across the heat exchanger before being exhausted from the air handling unit. The heat exchanger will transmit heat energy from the recirculating second air stream to the cooled first air stream, thereby reducing the sensible heat of the second air stream. However, because the saturated first air stream does not come into contact with the recirculating second air stream, the humidity of the second air stream will not be affected.

The above summary is not intended to describe each illustrated embodiment or every possible implementation. These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings.

IV. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a prior art air-side economizer.

FIG. 2 is a schematic view of an embodiment of the air handling unit of the present invention configured for operation in forced economization mode.

FIG. 3 is a schematic view of an embodiment of the air handling unit of the present invention configured for operation in full economization mode.

FIG. 4 is a schematic view of another embodiment of the air handling unit of the present invention configured for operation in full economization mode.

FIG. 5 is a schematic view of another embodiment of the air handling unit of the present invention configured for operation in full economization mode.

FIG. 6 is a schematic view of an embodiment of the air handling unit of the present invention configured for operation in partial economization mode.

V. DESCRIPTION

A preferred embodiment of the air handling unit 100 of the present invention is shown in FIGS. 2-4. The air handling unit 100 comprises a humidifier 110 positioned in a first air stream 190 and a heat exchanger 120 positioned partially in the first air stream 190 and partially in a second air stream 191.

In the preferred embodiment depicted in FIGS. 2-4, the humidifier 110 is an evaporative humidifier, and the heat exchanger 120 is a heat pipe. The heat pipe 120 can comprise a cold deck portion 121 disposed within a first duct 105, and a hot deck portion 122 disposed within a second duct 106. The heat pipe, and the first and second ducts 105, 106 in which the heat pipe is mounted, can be installed in either a vertical or horizontal orientation. In alternative embodiments, the heat exchanger 120 can be a heat wheel, a fixed-plate exchanger, or other known energy recovery mechanism. The humidifier 110 can be an ultrasonic humidifier, a spray mist humidifier, a steam vaporizer, a drum style humidifier, a disc wheel style humidifier, or any other known means for humidifying air.

Air is circulated from the air handling unit 100 to a conditioned space by means of a supply fan 150, while air is exhausted from the air handling unit 100 by means of an exhaust fan 160. In certain embodiments, the air handling unit can also feature an integrated mechanical cooling device 140 to supplement the free cooling provided by the air handling unit 100. A plurality of dampers 130, 131, 132, 133, 134 control the flow of air through the air handling unit 100. A computerized control system can be used to monitor the outside air conditions and automatically change configurations, or modes, of the air handling unit 100 to maximize the free cooling potential of the climate while maintaining the integrity of the conditioned space.

FIG. 2 shows a schematic view of the air handling unit 100 configured in a forced economization mode. The air handling unit 100 will operate in a forced economization mode when the outside air is above the targeted dew point for the conditioned space. The humid outside air is not suitable for being circulated into the conditioned space, but nevertheless can be utilized as a cooling media so long as the air is not 100% saturated in its natural state. In this mode, the first air stream 190 comprising outside air will be routed successively through the outside air inlet 101, through the evaporative humidifier 110, through open damper 132, through the cold deck portion 121 of the heat pipe 120, and then exhausted by the exhaust fan 160 through the exhaust air outlet 102. The outside air stream 190 will be humidified up to the air's saturation point as it circulates through the evaporative humidifier 110, thereby cooling the outside air stream 190 up to approximately (e.g., within 2%) its adiabatic saturation temperature before it is circulated through the heat pipe 120. Meanwhile, the inside air will be in recirculation mode. A second air stream 191 comprising recirculating inside air will be routed successively through the return air inlet 103, through open damper 133, through the hot deck portion 122 of the heat pipe 120, through the mechanical cooling device 140, through the supply fan 150, and out the supply air outlet 104 and into the conditioned space. As the recirculating inside air stream 191 goes through the hot deck portion 122 of the pipe 120, heat energy will be transmitted from the recirculating inside air stream 191 to the outside air stream 190, thereby reducing the temperature (i.e., the sensible heat) of the inside air stream 191. Through this process, the inside air stream 191 will be cooled to its lowest possible free cooling condition. If additional cooling is needed, the control system can activate the mechanical cooling device 140 to further cool the inside air stream 191 to the target supply air temperature. In this mode, the humidity of the controlled space should not be affected since the humidified outside air stream 190 does not come into contact with the recirculating inside air stream 191. While there may be some air leakage through closed dampers 130, 131, and 134 (leak rate for current-generation dampers being approximately 3 CFM/sq.ft) in this mode, such leakage is negligible. There will be substantially no exchange of moisture between the outside air stream 190 and the inside air stream 191, thereby allowing the dew point of the recirculating inside air stream 191 to remain substantially unchanged.

FIGS. 3-5 show schematic views of the air handling unit 100 configured in a full economization mode. The air handling unit 100 will operate in a full economization mode when the outside air temperature and dew point are at or below the targeted supply air temperature and dew point. In this mode, the air handling unit 100 can satisfy the cooling load without any mechanical cooling, thereby allowing the mechanical cooling device 140 to be deactivated. The control system will modulate the air dampers 130, 131, 133, 134 to obtain the desired supply air temperature and humidity. For instance, if the outside air conditions are ideal, the first damper 130 can be opened fully and the conditioned space can be cooled with 100% outside air (See FIG. 3). If the outside air stream 190 is too cool, then the first damper 130 and the fourth damper 133 can be modulated to achieve the appropriate mix of cool outside air and warm return air (See FIG. 4). If the outside air stream 190 is too dry, then the second damper 131 can be opened to direct the outside air stream 190 through the evaporative humidifier 110 before being supplied to the conditioned space (See FIG. 5).

FIG. 6 shows a schematic view of the air handling unit 100 configured in a partial forced economization mode. The air handling unit 1 will operate in a partial forced economization mode when the outside air is above the targeted supply air temperature but below the targeted dew point. In this mode, the outside air stream 190 will be routed through a two-stage cooling system. The first stage involves the circulation of the outside air stream 190 through the evaporative humidifier 110 to humidify the outside air to the targeted level. As discussed above, the humidification of the outside air stream 110—an adiabatic process—will result in a proportional drop in temperature. The second stage, if necessary, involves the circulation of the outside air stream 190 through the mechanical cooling device 140 to further cool the outside air stream 190 before it is supplied to the conditioned space.

Many modifications and other embodiments of the invention set forth herein will come to mind to one skilled in the art having the benefit of the teaching presented in the foregoing description and associated drawings. For instance, in FIGS. 2-4, the evaporative humidifier 110 and the exhaust fan 160 are shown as being installed within the first duct 105, while the mechanical cooling device 140 and the supply fan 150 are shown as being installed within the second duct 106. However, one skilled in the art will appreciate that the foregoing components can be installed in separate, interconnected ducts in an alternative embodiment. Further, although the air handling unit of the present invention is described for use as a cooling system for data centers, the present invention can be utilized as a cooling system for any conditioned space. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation. 

1. An air handling unit for conditioning air, comprising: a. A humidifier positioned in a first air stream for humidifying the first air stream; and b. A heat exchanger positioned partially in the first air stream and partially in a second air stream, the heat exchanger capable of transferring heat from the second air stream to the first air stream.
 2. The air handling unit of claim 2, wherein the first air stream comprises outside air, and wherein the second air stream comprises recirculated inside air.
 3. The air handling unit of claim 2, wherein the humidifier cools the first air stream up to its adiabatic saturation temperature.
 4. The air handling unit of claim 3, wherein the heat exchanger is positioned partially within a first air duct and partially within a second air duct.
 5. The air handling unit of claim 4, wherein the humidifier is positioned within the first air duct.
 6. The air handling unit of claim 6, wherein the humidifier is positioned within a separate air duct connected to the first air duct.
 7. The air handling unit of claim 4, wherein the first air stream flows through the first air duct, and wherein the second air stream flows through the second air duct.
 8. The air handling unit of claim 7, wherein the heat exchanger comprises a first portion positioned within the first air duct, and a second portion positioned within the second air duct.
 9. The air handling unit of claim 8, further comprising a supply fan for circulating the cooled second air stream within a conditioned space.
 10. The air handling unit of claim 9, further comprising an exhaust fan for discharging the humidified first air stream from the air handling unit.
 11. The air handling unit of claim 10, further comprising a mechanical cooling device positioned in the second air stream for further cooling the second air stream before the second air stream is recirculated by the supply fan within the conditioned space.
 12. The air handling unit of claim 11, wherein the first air duct comprises an outside air inlet and an exhaust air outlet, and wherein the second air duct comprises a return air inlet and a supply air outlet.
 13. The air handling unit of claim 12, wherein the supply fan circulates the second air stream successively through the return air inlet, the second portion of the heat exchanger, the mechanical cooling device, and the supply air outlet.
 14. The air handling unit of claim 13, wherein the exhaust fan circulates the first air stream successively through the outside air inlet, the humidifier, the first portion of the heat exchanger, and the exhaust air outlet.
 15. The air handling unit of claim 15, further comprising a plurality of dampers for controlling the flow of air in the air handling unit.
 16. The air handling unit of claim 7, wherein the heat exchanger is a heat pipe, the heat pipe comprising a cold deck portion and a hot deck portion, wherein the cold deck portion is positioned within the first air duct, and wherein the hot deck portion is positioned within the second air duct.
 17. The air handling unit of claim 7, wherein the heat exchanger is a heat wheel.
 18. The air handling unit of claim 7, wherein the humidifier is an evaporative humidifier.
 19. The air handling unit of claim 3, wherein there is substantially no exchange of moisture between the first air stream and the second air stream.
 20. The air handling unit of claim 3, wherein the dew point of the second air stream remains substantially unchanged.
 21. An air handling unit for conditioning air, comprising: a. a humidifying means positioned in a first air stream for humidifying the first air stream up to its adiabatic saturation temperature; and b. A heat exchanger positioned partially within the first air stream and partially within a second air stream, the energy recovery heat exchanger cooling the second air stream using the humidified first air stream, wherein there is substantially no exchange of moisture between the first air stream and the second air stream.
 22. The air handling unit of claim 21, wherein the humidifying means is selected from the group consisting of an evaporative humidifier, an ultrasonic humidifier, a spray mist humidifier, a steam vaporizer, a drum style humidifier, and a disc wheel style humidifier.
 23. The air handling unit of claim 21, wherein the heat exchanger is selected from the group consisting of a heat pipe, a heat wheel, and a fixed-plate exchanger.
 24. A data center comprising: a. a conditioned space housing electronic equipment; b. an air handling unit for conditioning the air in the conditioned space, the air handling unit comprising: i. a humidifier positioned in a first air stream, the humidifier capable of cooling the first air stream up to its adiabatic saturation temperature by humidifying the first air stream; and ii. A heat exchanger positioned partially within the first air stream and partially within a second air stream, the energy recovery heat exchanger cooling the second air stream using the humidified first air stream; c. an exhaust fan positioned in the first air stream for discharging the humidified first air stream from the air handling unit; and d. a supply fan positioned in the second air stream for circulating the second air stream within the conditioned space.
 25. The data center of claim 24, wherein the heat exchanger is positioned partially within a first air duct and partially within a second air duct.
 26. The data center of claim 25, wherein the first air stream flows through the first air duct, and wherein the second air stream flows through the second air duct.
 27. The air handling unit of claim 26, wherein there is substantially no exchange of moisture between the first air stream and the second air stream.
 28. The air handling unit of claim 26, wherein the dew point of the second air stream remains substantially unchanged.
 29. A method for cooling a conditioned space, comprising: a. Providing an air handling unit for conditioning the air in the conditioned space, the air handling unit comprising a humidifier and a heat exchanger, the heat exchanger defining a first portion and a second portion; b. Circulating an outside air stream successively through the humidifier and the first portion of the heat exchanger; c. Circulating an inside air stream through the second portion of the heat exchanger to cool the inside air stream; and d. Supplying the inside air stream to the conditioned space.
 30. The method of claim 29, wherein the circulated inside air is further cooled by a mechanical cooling device before the circulated inside air is supplied to the conditioned space. 